In general, as one of protocols for performing path control of an IP network, an open shortest path first (OSPF) protocol has been used. In OSPF, routers exchange path control information called link state advertisement (LSA) with one another, thereby constructing a routing table so as to perform path control. LSA has information on cost, which serves as a determination criterion for determining a path when each router constructs a routing table.
In a routing protocol, such as OSPF, each router determines a path in an IP network by using information, such as information on cost that is calculated based on the bandwidth of a line, and the like as a determination criterion. For example, each router derives a path for which the cost of a path through which information transmitted from a transmission source to a destination passes is minimized, and sets the derived path in a routing table, thereby determining a path in the IP network.
Depending on the scale and configuration of an IP network, there are cases in which a plurality of paths each having cost (for example, a minimum cost) serving as a determination criterion for determining a path exist. Such paths form what is called an equal cost multi path (ECMP).
When a routing table is to be constructed, in the case that information that is transmitted from the transmission source to the destination passes through an ECMP, each router sets, in the routing table, a plurality of paths that constitute an ECMP as paths corresponding to flows from the transmission source to the destination. Then, when the information from the transmission source to the destination, which passes through the ECMP, is transmitted, each router determines a path through which the information passes from among a plurality of paths constituting an ECMP based on a certain rule for routing the path.
FIG. 24 illustrates an example of the configuration of a typical IP network.
FIG. 25 illustrates a routing table T5 in a typical IP network 100 illustrated in FIG. 24.
In the IP network 100 illustrated in FIG. 24, reference characters A to J denote relay devices, such as routers.
The numerical values positioned between the routers, illustrated in FIG. 24, denote costs between the routers. Furthermore, each of the routers A to J generates a routing table based on information, such as cost included in the LSA exchanged between the routers.
For example, in the configuration of the IP network 100 illustrated in FIG. 24, each of the routers A to J sets a path in the routing table T5 illustrated in FIG. 25 so that the flow from the subnetwork 10.0.0.0/8 to the subnetwork 12.0.0.0/8 passes through the path A→C→E→G→I in which the cost is a minimum (40).
Furthermore, each of the routers A to J sets a path in the routing table T5 so that the flow from the subnetwork 10.0.0.0/8 to the subnetwork 13.0.0.0/8 passes through either the path A→C→E→G→H→J or the path A→C→D→F→H→J, in which the cost is a minimum (70).
At this time, the path A→C→E→G→H→J and the path A→C→D→F→H→J are paths of ECMP.
Hereinafter, similarly, the path of each flow is set based on LSA for each of a transmission source subnetwork and a destination subnetwork.
A failure path monitoring apparatus (apparatus for monitoring a path) 110 illustrated in FIG. 24 is an apparatus that is disposed in the IP network 100 and that monitors data transmitted in the IP network 100 so as to identify the path in which a failure has occurred when the quality of data has deteriorated.
Here, whether the data that is transmitted from the subnetwork 10.0.0.0/8 to the subnetwork 13.0.0.0/8 actually passes through one of the paths of the ECMP, in the manner described above, depends on a certain rule for routing the path in the routers A to J. As described above, the routing of the path in each of the routers A to J is determined inside the routers A to J. Therefore, it is difficult to easily identify which one of the paths of ECMP the data passes through based on the information included in the data that passes through the ECMP of the IP network 100.
For example, when a failure occurs in a section of an ECMP in the IP network 100 and the quality of the flow from the subnetwork 10.0.0.0/8 to the subnetwork 13.0.0.0/8 deteriorates, the failure path monitoring apparatus 110 determines the path through which the data in which the deterioration of quality has occurred passed in order to identify the path in which the failure has occurred.
For this purpose, the failure path monitoring apparatus 110 determines the path through which the data passed by referring to, for example, the routing table T5 based on the information of the transmission source subnetwork 10.0.0.0/8 and the destination subnetwork 13.0.0.0/8 of the data in which the deterioration of quality has occurred.
Then, the failure path monitoring apparatus 110 obtains, based on the routing table T5, information indicating that the data transmitted from the subnetwork 10.0.0.0/8 to the subnetwork 13.0.0.0/8 passed through one of the path A→C→E→G→H→J and the path A→C→D→F→H→J.
As described above, the failure path monitoring apparatus 110 monitors the data that is transmitted in the IP network 100 and determines that the path through which the data passed is an ECMP by referring to the routing table T5.
However, in the manner described above, the routing of the path in each of the routers A to J is determined inside the routers A to J.
Therefore, it is difficult for the failure path monitoring apparatus 110 to easily identify which one of the ECMPs the data in which the deterioration of quality has occurred passed through actually based on the information included in the data that passed through the ECMP of the IP network 100.
As a result of the above, when the quality of data deteriorates in a path of an ECMP, it is desired to quickly identify the path in which the deterioration of quality has occurred.
Hitherto, in order to identify a path in which the quality of data has deteriorated in an ECMP, the failure path monitoring apparatus 110 has performed a path search, such as traceroute, for each IP address between the transmission source subnetwork and the destination subnetwork of the data in which the deterioration of quality has occurred. Then, the failure path monitoring apparatus 110 has confirmed which path the flow of each of the transmission source IP address and the destination IP address in the transmission source subnetwork and the destination subnetwork of the data in which the deterioration of quality has occurred passed through, and has performed a quality measurement on each flow for which the passed path has been confirmed, thereby identifying the path in which the deterioration of quality has occurred.
There is a known method in which, in order to identify a failure occurrence place in the path of a communication network, a monitoring apparatus obtains quality information for each flow from each terminal that exists in the communication network, and estimates a quality deterioration place by using various algorithms based on path information obtained from a router or the like.
There is another known method in which a monitoring apparatus generates a table indicating a hierarchical structure based on a network topology, and finds a branch at which a failure has been detected in all the terminals on the lower layer side based on this table and information on the failure detection place, thereby estimating the branch as a failure occurrence place.
However, in the above-described technique for identifying a path in which the deterioration of quality of the data has occurred in an ECMP, since traceroute is performed for each of a transmission source IP address and a destination IP address, much time is taken to identify the path for each IP address. Furthermore, in the path in which the quality of data has deteriorated, there is a case in which the execution result of traceroute cannot be received.
On the other hand, in the known technique described above for identifying a failure occurrence place in the path of the communication network, in an IP network in which OSPF is used, it is difficult to easily identify a failure path in the ECMP section.